Evolution of Human: From Australopithecus to Homo Sapiens

The theory of evolution by natural selection explains how organisms change over time. The evolution of human has been a result of changes in physical and behavioural traits. The brain size, teeth size, shape of forehead, and brow ridges have all undergone changes during the course of evolution. Fossils of hominid are found only in Africa, and stone tools are found in association with Homo erectus. Nomadic people hunt and gather food, while sedentary people practice agriculture. Recent discoveries include Homo naledi fossil, Homo sapiens fossils from Morocco, and Nyanzapithecus alesi.

HUMAN EVOLUTION

1.) EVOLUTION OF HUMAN
The theory of evolution by natural selection is a process by which the organisms change over
time, as a result of changes in heritable physical or behavioural traitswhich allows them to
adopt and survive in the environment. This extraordinary theory has two main aspects
according to Brian Richmond, “All life on Earth is
connected and related to each other,”
(Alexander,2015) and as a result of this mixture in
life "modifications of populations by natural
selection, where some traits were favoured in and
environment over others,” 1. Furthermore, looking at
(Figure 1) similar ear structure and heavy bones
have been evident between whales and
“Indohyus”(close relative to whales)that haveaquatic
lifestyle, indicates similar traits to whales2, which
also allowed them to submerge for four minutes to
avoid predators and be able to less buoyant,. As a
consequent of organism’s connectivity due to sex
and mutation, whales ancient ancestors “pakicetids”
known from 50-million-year-old fossil had four legs
and tails which, might have looked similar to wolves
than whales due to the environment they lived in
whichfurther explains modifications of populations
by natural selection2. The two aspects mentioned earlier are Charles Darwin’s contribution to
the theory of evolution however, Alfred Wallace played a pivotal role in developing his
theory. Darwin’s theory developed during the time he spend on Galapagos island which then
led him to understanding of transmutation among the living species3. However,heobserved
the absence of several species compared to ahigh number of endemic species living on the
island which was the main focus in his book called “On the Origin of Species”3. According to
the comparison between living species on the island it was concluded thatsurvival of the
fittestincreases probabilities of living for those who altered their traits according to their
environment3 which is evident by body and trace fossils (Geary, 2017). Fossils are the
FIGURE 1THE WHALE EVOLUTIONARY TREE

naturally protected body remaining of animals or plants that lived in the geologic past4.
Fossils are formed through different conditions however, mainly fossilisation occurs in a
process called petrification where skin and bones completely decompose leaving a cast of
organisms. All the found fossils of hominid are in a complex nexus of specimens, which
allows scientists to examine and study the changes occurred to brain, body size, locomotion
and other aspects of life over the past 6 million years ago6. Moreover, examining figure
3,bipedalism and alike spinal cord structure between homo, Paranthropus, Australopithecus
and Ardipithecus groupssupport changes in heritable physical traits (evolution theory) that
links them in Phylogenetic tree (figure 2)
FIGURE 2
PHYLOGENETIC TREE

FIGURE 3 SKELETON STRUCTURE
French palaeontologist Michael Brunet lead a research team in 2001 where they uncovered
fossils of Sahelanthropus in West-Central Africa that belongs to approximately 7 million
years ago7. Thus, Brunet’s discovery proves that our ancestors were not only distributed
around the Great Rift Valley in East Africa however, more widely spread across Africa
around West-Central Africa7. Sahelanthropus had combination traits of ape-like features such
as small brain (even smaller than chimpanzee), sloping face, prominent brow ridges, and
elongated skull and human-like features such as small canine teeth, a short middle of the face,
and a spinal cord opening underneath the skull instead of towards the back as seen in non-
bipedal apes7. However, Homo sapiens evolution started in Africa approximately 300,000
years ago8. Anatomically, modern humans skeleton has a lighter bone structure compared to
early human due to our sedentary life style (Gifford, 2018).
Section 2
Examining figure 4 and 5, transformation of brain structure and size demonstrates changes in
physical and behavioural traits that allowed them to face new environmental challenges.
Thisbody adoption advanced their social interactions and unfamiliar habitats9. During the
course of human evolution brain size tripled to a more complex shape which is due to
variation of temperature (Dobzhansky, 2012). Graph 1 demonstrates the alternation of
temperature over the past 3 million years ago and during the greatest climate change the
greatest brain size increase occurs in ectotherms and endotherms. This is due to aerobic
capacity which is the main factor in physical performance, allows the brain to exponentially
grow10.

FIGURE 4 ENDOCASTS OF HOMO ERECTUS (LEFT) AND HOMO SAPIENS (RIGHT)
DISPLAYS RAPID INCREASE BRAIN SIZE
FIGURE 5 DIFFERENT BODY STRUCTURE

GRAPH 1
2.) To understand the full process of evolution of humans ,there is need to study one by
one the physical changes which occurred during the evolution
EVOLUTION OF BRAIN
With the evolution of hominine, brain size was keep on increasing thus intelligence was
increasing. Australopithecus was having brain capacity of 440cc. Early fossils show that
Homo habilis were having brain capacity of 700cc. Thereafter, Homo erectus , which are also
known as Java man , were having brain capacity of 950cc (Cavalli-Sforza and Cavalli-Sforza,
2016). Homo sapiens (Swanscombe) who were present 0.25 million years ago were having
brain capacity of 1200cc and Neanderthal, which were present before 0.08million years were
having 1500cc of brain capacity.

TOOTH SIZE
Early ancestors of Homo sapiens, that is, dryopethicus and ramapethicus were herbivorous
who were dependent on fruits and leaves. But from Australopethicus africanus , they were
carnivorous and were dependent on the animal flesh (Murphy, 2012). During the course of
evolution after that, Homo erectus came out to be omnivorous. These change in the habit of
food leads to evolution of teeth of the hominine.
Following table shows the evolution of teeth during the course of evolution of hominine-
No. GENUS TEETH TYPE
1 Dryopethicus Large canines, incisors, square molars
2 Ramapithecus Small canines, flattened molars, thicker enamel
3 Australopithecus afarensis Small canines and incisors
4 Austrlopithecus africanus Small canines
5 Homo habilis Small canines
6 Homo erectus( java man) Small canines

7 Homo sapiens Small canines
8 Neanderthal Heavier than modern teeth, wisdom teeth.
SHAPE OF FOREHEAD
Homo sapiens clade was heaving endocranial shape similar of Homo erectus and
Neanderthals (Alexander, 2017). Younger Homo sapiens, the frontal area becomes taller,
parietal area bulged out, occipital area of the skull becomes rounder and side walls become
parallel. Both processes resulted in more globular shape.
EVOLUTION OF BROW RIDGES
Homo sapiens sapiens have very small eyebrows or almost no eyebrow. Eyebrows have no
function with chewing or hunting but it plays great role in expressing aggressiveness.
Chimpanzees and Australopithecus needed to hunt different animals for their food (Groves,
2015). For this purpose they need broader eyebrow ridges but with the evolution of
hominines they become omnivorous and tendency to hunt decrease ,therefore, no need of

eyebrows for showing aggressiveness ,therefore, modern man have almost negligible
eyebrows.
S.
NO.
CHIMPANZEE SKULL HUMAN SKULL
1 Size of chimpanzee was 400cc Brain capacity of human skull is 1400cc
2 Face of chimpanzee was Protruding
outwards
Human face is almost flat
3 Chimpanzees were having large canines,
incisors and square molars
Human teeth are small and relatively
regular in size throughout the jaw
4 Position of foramen magnum is towards
the back of the skull
Foramen magnum is facing directly
downwards
3.) Amongst A.boisie, H.habilis, Lucy, A.africanus and A.robustus , H.habilis is
different from the others. Except the H.habilis , all others are belonging from the
genus Australopithecus. Fossils of all, A.boisie, H.habilis, Lucy, A.africanus and
A.robustus were excavated from the Tanzania , Africa (Bowler, 2016). Their brain
size were lying between 500-600cc. They all were having large and powerful jaws
and therefore they were mainly dependent on the hard food sources. The all were
herbivores, that is, they ate fruits and leaves as their main diet.
4.) WHY AUSTRAOPITHECUS FOSSILS ONLY FOUND IN AFRICA
Before 3.5million years ago Australopithecus were wide spread throughout eastern and
Northern Africa. Evidence shows their presents at that time in Tanzania. Also their footprints
have been found near to Tanzania (McGrew and McGrew, 2012). Therefore, fossils of
Australopithecus were only excavated from Africa only and not from any other part of the
world.

5.) WHY STONE TOOLS ONLY FOUND IN THE LOCATION IN ASSOCIATION
WITH HOMO ERECTUS AND NOT WHERE AUSTRALOPITHECANS LIVING
Diet of Australopithecus was mainly herbivorous. They were also not much civilized. They
were having large jaws for the purpose of cutting and eating of the food. Further their I.Q.
was not that much to use any tools for their livelihood nor did they require. But when anyone
look to Homo erectus, their diet was omnivorous. They require hunting the animals. Further
their jaws were reduces and they need tools for crushing and cutting of food. Homo erectus
marks the beginning of the cultural evolution. They started using fire and other tools. These
are the reasons behind the findings of stone tools in locations which were associated with the
Homo erectus and no availability of stone or other kind of tools at the places which were
associated with Australopithecus.
6.) WHY AFRICAN GREAT APES USE KNUCKLE WALKING
Due to repetitive loads on the soft tissues due to impact loadings, there was change in the
musculature and the shape of hard tissues. This lead to change in the torso shape because of
which African great apes started to knuckle walk (Campbell, 2017). Adaptation to the
knuckle walking was in the carpals and meta carpals. There is also limited motions in the
wrist and hands of African great apes , which was also the reason behind the knuckle walking
as a means of locomotion.
7.) WHY NOMADIC PEOPLE ARE CONCEREND WITH THE HUNTING AND
GATHERING OF FOOD WHEREAS SEDENTRY PEOPLE DONOT DO THAT
Nomadic people are those who always keep on travelling. They do not have any fix place to
stay. Because of this, they can’t get food sources son easily. Whenever they shift to a new
place , they have to search for a new food source and for that reason they use hunting also.
On the other hand, Sedentary people were those who inhabit in the same locality throughout
their life (Alexander,2017).They do agricultural practices and have domestic animals.
Therefore, there is no nee of hunting and search for the food source because thy directly get it
from agriculture or from the domestic animals.
8.) RECENT DISCOVERIES OF THE FOSSILS OF HOMININ ANCESTORS
a. Homo naledi fossil
In the cave of South Africa, recovery of the new species called homo naledi was
done.(Washburn, 2016) They are having collar bone , legs and ankles similar to the
human beings. There were found from the dinaledi chamber of the rising star cave

system. In total there were fossils of 4 individuals were discovered among whom 1
was of child.
There are still some controversies with this discovery that, only 4 fossils which were
isolated from the cave wee available of this species (Wills, 2013). Further there was
no way or connection to that cave so that any individual can walk inside.
b. Homo sapiens fossils from Morocco which were 300,000 years old
Hublin and his team found the fossils of homo sapiens which were almost 300,00
years old. The age of fossils were determined with the help of radiometric dating.
Just like neanderthls, these were having similar faces , jaws and teeths which shos that
they were ancestors o human being. Whereas , their braincases wer elongated in
shape with ancesterol features which suggest they are not our encestors but a part of
African pan.
c. Nyanzapithecus alesi
The skull of an infant ape was found from the northern Kenya. It as estimated that the
skull is almost 13 million years old.this discovery help the researcher to know much
more about the cranial capacities , age of individuals whe they died, and about the
diest of them. With the help of X-rays of the teeth of the infant ape , it was determined
that for how much time did that infant survived untilll the nearby volcano erupted and
burrried the infant along with the forest

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